1. Field of the Invention
The present invention relates generally to the construction and use of vascular catheters and more particularly to systems and methods for exchanging vascular catheters having internal work elements over guidewires.
Atherosclerosis is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in the peripheral blood vessels, which feed the limbs of the body, and the coronary vessels, which feed the heart. When deposits accumulate in localized regions of a blood vessel, narrowing of the vascular lumen, referred to as stenosis, occurs. Blood flow is restricted and the person's health is at serious risk.
Numerous approaches for opening such stenosed regions are known, including balloon angioplasty, where a balloon-tipped catheter is used to dilate a stenosed region (optionally in combination with a stent for maintaining patency); atherectomy, where a blade, cutting element, or other abrasive element, is used to remove the atheroma or plaque; spark gap reduction, where an electric spark burns through the atheroma or plaque; and laser angioplasty, where laser energy is used to ablate at least a portion of the atheroma or plaque. In order to facilitate treatment of the stenosis with any of these approaches, it is often desirable to obtain an image of the interior of the blood vessel at the region to be treated. Catheters having imaging elements such as ultrasonic transducers are now gaining widespread acceptance for producing such images.
Of particular interest to the present invention, ultrasonic imaging catheters will often include an imaging core comprising ultrasonic imaging transducer or reflective element mounted on a rotatable drive shaft disposed within a flexible catheter body. The transducer, reflective element or both, can be rotated within the catheter body to direct an ultrasonic signal generally outward in order to scan the interior of the blood vessel wall. High resolution images revealing information concerning the extent and nature of the stenotic material can thus be produced.
During diagnostic, imaging, and interventional vascular procedures, it is often desirable to "exchange" one catheter for another. By "exchange" it is meant that one catheter is withdrawn from the vascular system and the another catheter is introduced to the vascular system. In order to maintain distal access, the exchange will usually be performed over a guidewire which is left in place to facilitate both catheter withdrawal and reintroduction of the new catheter.
Because of their excessive lengths, typically over 100 cm, the exchange of one catheter for another over a guidewire can be a complex procedure. In the early days of angioplasty and other vascular procedures, guidewire lumens were provided over the entire length of the interventional or other catheter. Thus, to permit withdrawal of the catheter over a guidewire which remains in place within the vascular system, the guidewire would have to be generally twice as long as the catheter (in order to allow the user to hold onto a proximal portion of the guidewire as the catheter is introduced thereover). In an effort to simplify catheter exchange, and in particular to reduce the necessary length of the guidewire, specialized catheter designs have been developed.
Such specialized catheter designs are now commonly referred to as "rapid exchange" designs, where the guidewire lumen does not extend the full length of the interventional or other catheter, but rather extends only from the distal tip to a side port which terminates a short distance proximally of the distal tip. In the case of long lumen rapid exchange catheters, the side port for the guidewire will typically be 10 cm or more from the distal tip of the catheter. Thus, the distal end of the catheter which enters the most tortuous regions of the vasculature will usually be reinforced by the internal guidewire (which engages the catheter over the entire length of the catheter which lies within the coronary arteries), preventing buckling and prolapse. The extended length of the guidewire lumen, however, generally requires that the distal dimensions of the catheter be increased to accommodate both the guidewire and the interventional or imaging component of the catheter.
Short lumen rapid exchange catheter designs (often referred to as "monorail" designs) generally employ a much shorter guidewire lumen at the distal end of the catheter, typically in the range from about 1 cm to 4 cm. The interventional, imaging, or diagnostic component of the catheter may then be disposed proximally up the guidewire lumen, allowing a reduction in the cross-sectional area of the catheter.
While such short lumen rapid exchange designs have proven to be very valuable, particularly for introduction of catheters to very small blood vessels, the provision of a side port so close to the distal end of the catheter can mechanically compromise the catheter. This is a particular problem where the catheter carries a relatively stiff internal component, such as an ultrasonic imaging core, proximal to the guidewire side port. The location of the weakened side port immediately distal to the imaging core will frequently cause the catheter to kink or prolapse as it passes over the guidewire through a relatively tight bend or curve in the vasculature.
For these reasons, it would be desirable to provide catheter systems and catheter sheaths for use with internal work elements, such as imaging cores, which have a short lumen rapid exchange design for receiving guidewires but which are resistant to kinking or prolapse when introduced through tortuous regions of the blood vessels. It would be particularly desirable if such catheter systems and sheaths were reinforced in the region of the guidewire side port in such a way that the cross-sectional area of the guidewire is not increased and the ability to introduce the catheter sheath or system over a guidewire is not compromised. Such catheter systems and sheaths should be compatible with catheters having internal work elements, particularly internal imaging cores, so that combinations of the catheter sheath and internal work element can be introduced simultaneously over the guidewire to a target location within the vascular system.
2. Description of the Background Art
Vascular ultrasonic imaging catheters having rapid exchange designs are described in U.S. Pat. Nos. 5,201,316; 5,024,234; and 4,951,677 (FIGS. 17 and 17A). Catheter sheaths having guidewire side ports near their distal ends are described in U.S. Pat. Nos. 4,932,413; 4,824,435; and 4,552,554. A short lumen rapid exchange balloon dilatation catheter is described in U.S. Pat. No. 4,762,129. An ultrasonic imaging catheter having a common distal lumen and rapid exchange capability is described in U.S. Pat. No. 5,203,338. A monorail sheath catheter usable with an ultrasonic imaging core was described in a Product Development Update of InterTherapy, Costa Mesa, Calif., dated Fall 1990.